Why do most pocket AM radio receivers have shorter (non resonant) antennas

[ofosot69]

I would like to know why most pocket radios come with a shorter whip antenna of about 20 cm, which is not a resonant one for FM or SW bands. So, how come they work like that?

 

[Martaine2005]

Probably something to do with the title. A pocket radio.
A metal coat hanger also works as an antenna but isn’t designed to be one.

 

[Alec_t]

I doubt there'd be much call for 'pocket' radios with a 2 metre long antenna sticking out.
The 20cm whip may well have a base-loading coil to increase its effective length..